The objective of the proposed research plan is to continue efforts begun in Phase I to develop an acoustic monitoring device for laser lithotripsy. In-vitro results to date have shown considerable promise for acoustic monitoring as an extremely valuable, non- visual diagnostic for laser fragmentation of urinary and biliary tract calculi. The attendant acoustic signatures generated have been shown to be useful for guiding and pinpointing the laser delivery fiber, indicating an appropriate choice of laser power level, and discriminating the irradiation of a stone from healthy, soft tissue surrounding it. An acoustic monitoring system providing such information to the clinician performing laser lithotripsy would be of great value, especially in those applications where vision is problematic. The specific objectives of the Phase II effort are: (1) to complete critical remaining studies to better quantify and more firmly establish the correlation of the acoustic signatures with a wide range of relevant laser irradiation and stone conditions, (2) use the knowledge acquired in (1) to guide the engineering design requirements for an acoustic monitoring device, (3) arrive at a prototype design and test it through a series of in-vitro and in- vivo (animal) studies, (4) establish final design requirements based on input from practicing clinicians, and (5) make a prototype device available for piggy-back experiments on ongoing clinical trials of laser lithotripsy. In short, the proposed Phase II program has been designed to provide the necessary research and development for commercializing this device in a Phase III effort.